This invention relates generally to an equalizer employed in a recording and/or reproducing apparatus or in a communication transmission channel and, more particularly, to an automatic equalizer in which parameters may be automatically set to optimum values.
In general, in a recording and/or reproducing apparatus or in a transmission channel for a communication system, it is known to use an equalizer to equalize the transmission characteristics for diminishing distortion occurring in the transmission of analog signals or minimizing errors in the transmission of digital data. In magnetic recording and/or reproducing apparatus, such as audio or video tape recorders, equalizers are used for enhancing high-frequency characteristics to permit increasing the recording density of the magnetic tape in the recording system.
Conventionally, the operational characteristics of the equalizer are adjusted and fixed at the optimum values at the time of shipment of the particular piece of electronic apparatus.
In a rotary head type video tape recorder or digital audio tape recorder, a system is known for recording neighboring tracks with different recording azimuth angles, thereby eliminating the requirement for a guard band between adjacent tracks. This is the so-called inclined azimuth recording that is employed for realizing higher recording densities on the tape. In a video tape recorder or a digital audio tape recorder employing such inclined azimuth recording system, a tracking servo is usually applied for signal reproduction. There has been proposed, however, in Japanese Patent Publication No. 59-177712 (1984), a signal reproducing apparatus in which reproduction is performed without using tracking servo control. With such signal reproducing apparatus, first and second inclined tracks TR.sub.A, TR.sub.B are alternately formed at different recording azimuth angles on a magnetic tape 1.
In order to reproduce these tracks, a rotational magnetic head device, as shown in FIG. 2, is employed in which first and second playback rotary magnetic heads 2A, 2B having azimuth angles corresponding to the recording azimuth are mounted at an angular interval of 180.degree. on a tape guide drum 2. Each track of the magnetic tape 1 placed on the tape guide drum 2 over an angular extent of 180.degree. is alternatively traced a plural number of times, for example twice, by first and second playback rotational magnetic heads 2A, 2B.
As shown in FIG. 3, the playback signals obtained by the rotary playback magnetic heads 2A, 2B are supplied from a head changeover switch 3 via a playback amplifier 4 and an equalizer 5 to a signal processing unit 6.
The reproduced signals, represented in FIG. 4, are produced at an angular interval of 180.degree. from the magnetic heads 2A, 2B by changeover of head operating switch 3 so as to be processed by signal processing unit 6 to form correct playback signals, which are then output at a signal output terminal 7.
As is well known, in magnetic recording and/or reproducing apparatus the frequency characteristics of the playback system are caused to vary by many factors, such as fluctuations in the magnetic recording media or magnetic heads, changes in temperature or humidity, or timing changes.
Hence, sufficient operational reliability cannot be obtained with the use of a conventional equalizer that has fixed equalizer characteristics. On the other hand, providing an allowance in the equalizer characteristics for adjustment to take into account fluctuations in the playback system usually results in the lowering of the recording density by an amount corresponding to such preset allowance.
Furthermore, with a signal reproducing apparatus in which signal reproduction is performed without a tracking servo, each track on the magnetic tape is traced alternately by the first and second playback magnetic heads 2A, 2B over its complete length, so that each track corresponds to two tracings. In other words, the track-tracing relation is the same for every other head tracing but differs for two consecutive head tracings.
Thus, in the reproducing apparatus in which signal reproduction is performed without tracking control, equalizing characteristics for odd-numbered track tracings must be measured and set independently from those for even-numbered tracings. As might be expected, in order to implement equalization, the overall system cannot but be complicated.